Step 1: Prepare the Dough
In a large bowl, combine the flour, butter, and salt. Using your fingertips, a pastry blender, or a food processor, blend the mixture until it resembles coarse meal with pea-sized butter chunks.
Step 2: Incorporate Wet Ingredients
Add sugar, baking soda (pre-mixed with a teaspoon of lemon juice), egg yolks, and lemon zest to the flour mixture. Gradually incorporate the sour cream, mixing until a smooth, soft, and flexible dough forms. Be careful not to overwork the dough. If the dough feels sticky, add a bit more flour; if it’s too firm, add a touch more sour cream.
Step 3: Prepare the Walnut Filling
Grind the walnuts to your desired consistency. In a bowl, mix the ground walnuts with sugar, hot milk, and lemon zest until well combined. Set the filling aside.
Step 4: Shape the Rugelach
Take a portion of the dough and roll it out into a 9-inch circle. Using a knife or pizza cutter, slice the dough into eight equal triangles. Place a spoonful of the walnut filling at the widest part of each triangle. Starting from the wide end, roll each triangle towards the point, forming a rugelach shape. Arrange the rugelach on an ungreased cookie sheet.
Step 5: Bake and Finish
Bake the rugelach in a preheated oven at 350°F (175°C) for 9 to 12 minutes or until they are lightly golden brown. Remove from the oven and let them cool slightly. Dust with powdered sugar before serving.
Note: Another popular filling for cornulete is a plum or apricot jam. If the jam used in rugelach isn't thick enough, it can spread or leak out during baking, leading to a messier appearance and less filling inside the rugelach. To prevent this, use a jam with a thick, spreadable consistency or cook it down to reduce its moisture content before using it as a filling. This will help the jam stay in place, resulting in a well-formed rugelach with the jam neatly contained inside.
